Apparatus and method for exhaust gas posttreatment

ABSTRACT

The invention relates to an exhaust gas aftertreatment device for an internal combustion engine supercharged in two stages, having an oxidation catalyst, a particle filter, and a metering device for introducing a regeneration agent into an exhaust gas system, and to an associated method for exhaust gas aftertreatment. According to the invention, the metering device is arranged in the exhaust gas system between a high-pressure turbine and a low-pressure turbine which produce two-stage supercharging of the internal combustion engine.

PRIOR ART

The invention is based on an apparatus for exhaust gas posttreatment as generically defined by independent claim 1 and by an associated method for exhaust gas posttreatment.

In European Patent EP 1 066 454 B1, an apparatus for exhaust gas posttreatment for a supercharged internal combustion engine is described.

It is furthermore generally known that for thermal regeneration of a soot-laden diesel particle filter for a diesel engine, an exhaust gas temperature in the diesel particle filter is raised to at least 600-620° C. This temperature increase can be achieved in part by provisions internal to the engine, such as throttling or postponing the onset of either the primary injection or a burning postinjection. A further temperature increase can be achieved as a rule via an oxidation catalytic converter located upstream of the diesel particle filter. To that end, either inside the engine via a late, nonburning postinjection or by means of metering downstream of the engine, a regeneration agent, such as uncombusted fuel, is introduced into the exhaust gas.

From a functional standpoint, a nonburning postinjection has the advantage that the introduced fuel, virtually ideally mixed, can act on the oxidation catalytic converter, and as a result the catalytic surface area of the oxidation catalytic converter can be optimally utilized. However, the nonburning postinjection causes pronounced thinning of the oil, as a result of which the oil change intervals have to be shortened drastically. Another disadvantage of the nonburning postinjection is in principle that the engine in this operating mode has a desired, very high emission of hydrocarbons, and the exhaust gas recirculation valve has to stay closed during the regeneration mode of the diesel particle filter, since otherwise, fuel would be undesirably delivered to a combustion chamber via the fresh-air supply, causing the engine to “race”. However, the requisite shutoff of the exhaust gas recirculation can cause a sharp rise in NOx emissions during the regeneration of the diesel particle filter, which can have an adverse effect on the certification of the vehicles if the regeneration periods are frequent or long. The nonburning postinjection is therefore difficult to achieve, particularly in utility vehicles.

For the mode of post-engine metering, there are basically two installation positions in conventional supercharged engines: upstream or downstream of a turbocharger. In metering upstream of the turbocharger, virtually ideal thorough mixing is obtained by the turbine, as in the nonburning postinjection. However, once again there is the danger of fuel recirculation by way of the exhaust gas recirculation. A further difficulty of this metering position is due to the usually quite high exhaust gas temperature at the engine outlet manifold. To protect a metering valve, high cooling power is as a rule necessary at the installation site upstream of the turbine. Metering downstream of the turbocharger solves the problems of fuel recirculation by way of the exhaust gas recirculation and makes cooling the metering valve easier. However, if the metering position is downstream of the turbocharger, the active thorough mixing by the turbine has to be dispensed with, and as a result, a uniform imposition of fuel on the oxidation catalytic converter cannot be assured; the efficiency can consequently diminish, and increased slippage of regeneration agent can occur.

DISCLOSURE OF THE INVENTION

The exhaust gas posttreatment apparatus according to the invention for an internal combustion engine with two-stage supercharging, having the characteristics of independent claim 1, has the advantage over the prior art that a metering device for introducing a regeneration agent is disposed in the exhaust gas system between a high-pressure turbine and a low-pressure turbine. By the disposition of the metering device in the manner according to the invention, good mixing of the exhaust gas and regeneration agent is advantageously attained for the sake of high efficiency of an oxidation catalytic converter, which is used for raising the temperature for thermal regeneration of a soot-laden particle filter. Moreover, the return of fuel via an exhaust gas recirculation line is advantageously prevented, since the exhaust gas recirculation line and the metering device are separated from one another by the high-pressure turbine. A further advantage of the disposition according to the invention of the Metering device results from the fact that the high-pressure turbine draws enthalpy from the exhaust gas, and as a result, compared to a disposition at the engine outlet manifold, the exhaust gas at the metering device is cooled markedly, so that cooling the metering valve entails less effort and expense.

The method for exhaust gas posttreatment according to the invention of an internal combustion engine with two-stage supercharging, having the characteristics of independent claim 5, has the advantage over the prior art that a regeneration agent for thermal regeneration of a soot-laden particle filter is introduced into the exhaust gas system between a high-pressure turbine and a low-pressure turbine, and an optimal exhaust gas posttreatment can be achieved without additional components, merely by utilizing the structural makeup of the exhaust gas system.

By the provisions and refinements recited in the dependent claims, advantageous improvements to the apparatus for exhaust gas posttreatment recited in independent claim 1 and the associated method recited in independent claim 5 are possible.

It is especially advantageous that the metering device is disposed upstream of the low-pressure turbine in such a way that the latter effects uniform thorough mixing of the regeneration agent and the exhaust gas in the exhaust gas system. This means that the low-pressure turbine, downstream of the metering device in the exhaust gas system, is advantageously utilized as an active mixer element.

In a feature of the apparatus according to the invention for exhaust gas posttreatment, at least one temperature sensor, which is evaluated for adjusting the metering device, is disposed in the exhaust gas system. Alternatively or in addition, a pressure difference sensor can present, which determines the pressure difference above the particle filter, from which difference a load state of the particle filter can be ascertained.

In a feature of the method of the invention for exhaust gas posttreatment, the introduction of the regeneration agent into the exhaust gas system can be effected such that the low-pressure turbine effects uniform thorough mixing of the regeneration agent and the exhaust gas in the exhaust gas system, and as a result, the oxidation catalytic converter disposed in the exhaust gas system is uniformly subjected to reducing agent.

Exemplary embodiments of the invention are shown in the drawings and will be described in further detail in the ensuing description.

BRIEF DESCRIPTION OF THE DRAWINGS

The sole drawing FIGURE is a block diagram of an exhaust gas posttreatment apparatus according to the invention for an internal combustion engine that is supercharged in two stages.

EMBODIMENT(S) OF THE INVENTION

As can be seen from the drawing, an exhaust gas posttreatment apparatus 1 according to the invention for an internal combustion engine 2 supercharged in two stages includes an oxidation catalytic converter 3, a particle filter 4, and a metering device 7 for introducing a regeneration agent into an exhaust gas system 8. The two-stage supercharging of the engine 2 is necessary in particular to meet future limit values for emissions in the field of utility motor vehicles.

As can also be seen from the drawing, the structural makeup of the exhaust gas system of the engine 2 supercharged in two stages can be utilized to achieve optimal functionality of the oxidation catalytic converter 3, using regeneration agent metering downstream of the engine. Hence according to the invention, the metering device 7 is disposed in the exhaust gas system 8 between a high-pressure turbine 5 and a low-pressure turbine 6 that effect the two-stage supercharging of the engine 2. The metering device 7 is disposed upstream of the low-pressure turbine 6 in such a way that the low-pressure turbine 6 can be used as an active mixer element, which effects uniform thorough mixing of the regeneration agent and the exhaust gas in the exhaust gas system 8. By the disposition of the metering device 7 downstream of the high-pressure turbine 5, a return of the regeneration agent via an exhaust gas recirculation line 9 is prevented, since the exhaust gas recirculation line 9 and the metering device 7 are separated from one another by the high-pressure turbine 5. Furthermore, the high-pressure turbine 5 draws enthalpy from the exhaust gas, and as a result, compared to a disposition at the engine outlet manifold, the exhaust gas is cooled down markedly at the metering device 7, so that cooling the metering device 7 entails less effort and expense.

For adjusting the metering device 7 and thus adjusting the quantity of regeneration agent that is introduced into the exhaust gas system 8, in the exemplary embodiment of the invention shown, two temperature sensors 10, 11 disposed in the exhaust gas system 8 are evaluated; one temperature sensor 10 is disposed upstream of the oxidation catalytic converter 3, and one temperature sensor 11 is disposed downstream of the oxidation catalytic converter 3. For ascertaining the load state of the particle filter 4, the exhaust gas posttreatment apparatus 1 includes a pressure difference sensor 12, which determines the pressure difference above the particle filter 4. The pressure difference sensor 12 can also be evaluated for activating and/or adjusting the metering device 7. For thermal regeneration of the soot-laden particle filter 4, which is preferably a diesel particle filter, the regeneration agent, such as uncombusted fuel, is introduced via the metering device 7 into the exhaust gas system 8 between the high-pressure turbine 5 and the low-pressure turbine 6, and the low-pressure turbine 6, as already noted above, effects uniform thorough mixing of the regeneration agent and the exhaust gas in the exhaust gas system 8, as a result of which the oxidation catalytic converter 3, located downstream of the low-pressure turbine 6 in the exhaust gas system 8, is uniformly subjected to reducing agent and is operated at high efficiency.

The invention advantageously utilizes the structural makeup of the exhaust gas system of an internal combustion engine, supercharged in two stages, without additional components for achieving metering of the regeneration agent downstream of the engine, and particularly for utility motor vehicles, the invention makes a concept for certain, economical regeneration of a particle filter system available. 

1-6. (canceled)
 7. An exhaust gas posttreatment apparatus for an internal combustion engine, supercharged in two stages, comprising: an oxidation catalytic converter; a particle filter; a high-pressure turbine and a low-pressure turbine that effect the two-stage supercharging of the engine; and a metering device introducing a regeneration agent into an exhaust gas system, wherein the metering device is disposed in the exhaust gas system between the high-pressure turbine and the low-pressure turbine.
 8. The apparatus as defined by claim 7, wherein the metering device is disposed upstream of the low-pressure turbine in such a way that the low-pressure turbine effects uniform thorough mixing of the regeneration agent and the exhaust gas in the exhaust gas system.
 9. The apparatus as defined by claim 7, further comprising at least one temperature sensor which is disposed in the exhaust gas system and is evaluated for the adjustment of the metering device.
 10. The apparatus as defined by claim 8, further comprising at least one temperature sensor which is disposed in the exhaust gas system and is evaluated for the adjustment of the metering device.
 11. The apparatus as defined by claim 7, further comprising a pressure difference sensor which determines a pressure difference in the particle filter, from which difference a load state of the particle filter can be ascertained.
 12. The apparatus as defined by claim 8, further comprising a pressure difference sensor which determines a pressure difference in the particle filter, from which difference a load state of the particle filter can be ascertained.
 13. The apparatus as defined by claim 9, further comprising a pressure difference sensor which determines a pressure difference in the particle filter, from which difference a load state of the particle filter can be ascertained.
 14. The apparatus as defined by claim 10, further comprising a pressure difference sensor which determines a pressure difference in the particle filter, from which difference a load state of the particle filter can be ascertained.
 15. A method for exhaust gas posttreatment of an internal combustion engine supercharged in two stages, comprising the step of introducing a regeneration agent for thermal regeneration of a soot-laden particle filter into an exhaust gas system between a high-pressure turbine and a low-pressure turbine disposed therein.
 16. The method as defined by claim 15, wherein the introduction of the regeneration agent into the exhaust gas system is effected in such a way that the low-pressure turbine effects uniform thorough mixing of the regeneration agent and the exhaust gas in the exhaust gas system, and an oxidation catalytic converter disposed in the exhaust gas system is uniformly subjected to reducing agent. 